Invention relates to a multi-joint crank drive an internal combustion engine with at least one coupling member supported on a crankpin of a crankshaft for rotation about a coupling member rotation axis and at least one articulated connecting rod supported on a crankpin of an eccentric shaft for rotation about an eccentric rotation axis, wherein the coupling member is pivotally connected with a piston connecting rod of a piston of the internal combustion engine for pivoting about a piston connecting rod rotation axis, and is pivotally connected with the articulated connecting rod for pivoting about a articulated connecting rod rotation axis, and wherein a rotation axis of the eccentric shaft is situated above a rotation plane, which receives a rotation axis of the crankshaft and is perpendicular to at least one cylinder longitudinal center axis. The invention also relates to an internal combustion engine with a multi-joint crank drive.
The multi-joint crank drive of the above-mentioned type is for example part of the internal combustion engine but can also be used in other areas. The multi-joint crank drive includes the eccentric shaft, whose rotation angle can preferably be adjusted by means of an actuator, in particular in dependence of an operating point of the internal combustion engine. As an alternative the eccentric shaft can also be operatively connected with a crankshaft of the internal combustion engine and in this be driven by the internal combustion engine.
The multi-joint crank drive includes the coupling member, in particular a number of coupling members that correspond to the number of the pistons of the internal combustion engine. The coupling member or the coupling members are each rotatably supported on the corresponding crankpin of the crankshaft. Preferably the coupling member has two arms that protrude toward opposite sides over the crankshaft and which are provided at their ends with a pivot joint. The rotation axis of the coupling member about the crankshaft or about the crankpin of the crankshaft is referred to as coupling member rotation axis.
One of the pivot joints serves for pivotal connection with the piston connecting rod which connects one of the pistons of the internal combustion engine with the crankshaft via the coupling member. The rotation axis of this pivot joint is referred to as piston connecting rod rotation axis. Due to the pivotability of the coupling member the piston connecting rod rotation axis is not stationary but is displaced or pivoted together with the coupling member. One of the pivot joints serves for pivotal connection with the so-called articulated connecting rod, which is supported with its other end, which is opposite the coupling member, rotatably on the crankpin of the eccentric shaft. The rotation axis of this pivot joint is referred to as articulated connecting rod rotation axis, while the rotation axis of the articulated connecting rod on the crankpin of the eccentric shaft is hereinafter referred to as eccentric rotation axis.
The articulated connecting rod has for forming the pivot joints preferably two conrod eyes. The first conrod eye is a part of the pivot joint via which the articulated connecting rod interacts with the coupling member. The first conrod eye includes hereby for example a coupling pin or bearing pin, which is held on the coupling member. Analogously, the second conrod eye is a part of the pivot joint via which the articulated connecting rod is connected with the eccentric shaft. In particular the second conrod eye engages around at least regions of the crankpin of the eccentric shaft.
By means of the multi-joint crank drive the compression ratio in the cylinder that is respectively assigned to the piston can be adjusted, in particular in dependence on an operating point of the internal combustion engine and/or the current operating cycle. For adjusting the compression ratio the eccentric shaft is brought into an angular position, which corresponds to the desired compression ratio or the phase position between the eccentric shaft and the crankshaft is set to a defined value.
From the state of the art the publication DE 601 09 4342 T2 is known which describes an internal combustion engine with variable compression ratio and cylinder capacity. The publication DE 10 2012 007 465 A1 discloses an internal combustion engine in which the lateral distance between a rotation axis and a crankshaft and a third joint in relation to the maximal travel of the piston is at least −1.0.
Known multi-joint crank drives are usually configured so as to be optimized for mounting space. As a consequence the kinematically effective lengths of the multi-joint cranks drive in relation to the piston travel are comparatively small. The forces in the pivot joints of such a multi-joint crank drive are relatively great and have to travel over large pivot angles and with this a correspondingly long path. The generated friction work, which represents the product of force and traveled path and is converted into heat, is thus also high.